987,426 research outputs found
Optimal Quantization of TV White Space Regions for a Broadcast Based Geolocation Database
In the current paradigm, TV white space databases communicate the available
channels over a reliable Internet connection to the secondary devices. For
places where an Internet connection is not available, such as in developing
countries, a broadcast based geolocation database can be considered. This
geolocation database will broadcast the TV white space (or the primary services
protection regions) on rate-constrained digital channel.
In this work, the quantization or digital representation of protection
regions is considered for rate-constrained broadcast geolocation database.
Protection regions should not be declared as white space regions due to the
quantization error. In this work, circular and basis based approximations are
presented for quantizing the protection regions. In circular approximation,
quantization design algorithms are presented to protect the primary from
quantization error while minimizing the white space area declared as protected
region. An efficient quantizer design algorithm is presented in this case. For
basis based approximations, an efficient method to represent the protection
regions by an `envelope' is developed. By design this envelope is a sparse
approximation, i.e., it has lesser number of non-zero coefficients in the basis
when compared to the original protection region. The approximation methods
presented in this work are tested using three experimental data-sets.Comment: 8 pages, 12 figures, submitted to IEEE DySPAN (Technology) 201
Evaporation and Accretion of Extrasolar Comets Following White Dwarf Kicks
Several lines of observational evidence suggest that white dwarfs receive
small birth kicks due to anisotropic mass loss. If other stars possess
extrasolar analogues to the Solar Oort cloud, the orbits of comets in such
clouds will be scrambled by white dwarf natal kicks. Although most comets will
be unbound, some will be placed on low angular momentum orbits vulnerable to
sublimation or tidal disruption. The dusty debris from these comets will
manifest itself as an IR excess temporarily visible around newborn white
dwarfs; examples of such disks may already have been seen in the Helix Nebula,
and around several other young white dwarfs. Future observations with the James
Webb Space Telescope may distinguish this hypothesis from alternatives such as
a dynamically excited Kuiper Belt analogue. Although competing hypotheses
exist, the observation that of young white dwarfs possess such
disks, if interpreted as indeed being cometary in origin, provides indirect
evidence that low mass gas giants (thought necessary to produce an Oort cloud)
are common in the outer regions of extrasolar planetary systems. Hydrogen
abundances in the atmospheres of older white dwarfs can, if sufficiently low,
also be used to place constraints on the joint parameter space of natal kicks
and exo-Oort cloud models.Comment: 22 pages, 13 figures, published in MNRAS. Changes made to match
published versio
Adaptive nonparametric confidence sets
We construct honest confidence regions for a Hilbert space-valued parameter
in various statistical models. The confidence sets can be centered at arbitrary
adaptive estimators, and have diameter which adapts optimally to a given
selection of models. The latter adaptation is necessarily limited in scope. We
review the notion of adaptive confidence regions, and relate the optimal rates
of the diameter of adaptive confidence regions to the minimax rates for testing
and estimation. Applications include the finite normal mean model, the white
noise model, density estimation and regression with random design.Comment: Published at http://dx.doi.org/10.1214/009053605000000877 in the
Annals of Statistics (http://www.imstat.org/aos/) by the Institute of
Mathematical Statistics (http://www.imstat.org
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